As the quality of the world's water supply continues to decline, even in developed nations, due to increased man-made contaminants, the need to purify the water for drinking at the point of consumption, such as the home, is also dramatically increasing. Because of the types of contaminants found in today's water supply, such as pesticides, fertilizers, chemical solvents, and the like, one of the most effective ways of removing the same is by adsorbing or absorbing the contaminant by use of a sorbent bed through which the water is passed. Typical sorbent beds are made of activated carbonaceous material. Such activated carbon beds may be used in conjunction with a filtration medium, used to remove bacterial and microbial contamination from the water.
In most point-of-use water purification systems the sorbent bed is maintained in contact with residual water left in the system after each use. Further, typical sorbent media, and some filtration media, provide very good sites for microorganisms to accumulate and grow. The damp sorbent bed with its entrained contaminants can act as an ideal environment for colonization of microorganisms. Such microorganism growth can lead to very undesirable results.
The very water that is to be purified, may now be contaminated by the sorbent bed in the purification system. Further, the growth of the microorganisms is usually associated with the evolution of undesirable by-products, such as gaseous hydrogen sulfide, typically recognized by its "rotten-egg" odor. The presence of such by-products in potable water diminishes its aesthetic quality.
A problem has therefore arisen due to the undesirable microorganism growth on sorbent media in potable water purification systems. It has been known for many years that the presence of metal ions can be deleterious to the growth and survival of microorganisms, at high enough concentrations. However, it is not desirable to overcome the problem of microorganism contamination by introducing another problem, metal contamination of the potable water.
Although there are no uniform drinking water standards that must be met, the U.S. Environmental Protection Agency ("EPA") has established guidelines for the maximum concentration of certain metals in drinking water. For example, the EPA guideline for copper concentration is 1 ppmw and the EPA guideline for zinc concentration is 5 ppmw. The aforementioned solution of adding metal ions to the water to kill the microorganisms is not an acceptable solution if it in turn renders the water unfit for drinking.
Published PCT application PCT/US86/01996, published Mar. 21, 1987 under Publication Number WO 87/01688, discusses the use of particulate metal, such as brass, for treating water to remove undesirable constituents in water, such as chlorine. The application has as one of its objects the treatment of fluids wherein the fluids are first passed through a conventional fluid treating process such as an activated carbon process and then the fluid is passed through a bed of metal particulate matter to treat undesirable constituents, such as harmful bacteria. When specifically addressing the use of an activated carbon treating medium, the application states that it may be desirable to have the bed of particulate matter downstream of the activated carbon to treat any harmful bacteria contained in the fluid leaving the bed of activated carbon. The reference therefore does not recognize or address the problem solved by the present invention, reduction or inhibition of bacterial growth on the activated carbon itself. Treatment of the effluent from the activated carbon bed will not affect microorganism growth on the bed itself.
Heretofore nothing in the art has taught or suggested that it would be possible to prevent microorganism growth on sorbent media, such as activated carbon, through the introduction of metal ions to the influent water, while maintaining the concentration of such metal ions within acceptable limits for drinking water in the effluent.